Serradella - Part D Managing serradella

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Fertilisers

Although serradella is a deep rooted plant—and a good scavenger for nutrients such as phosphorus and sulphur—soil deficiencies need to be corrected if a productive stand is to be established and maintained. A sensible fertiliser program generally more than trebles serradella productivity.

Sulphur and phosphorus are likely to be the nutrients most commonly lacking in many light acidic soils. Research has shown that 10–20 kg/ha of phosphorus and 12–15 kg/ha of sulphur (example 120–150 kg/ha single super), applied every one to three years is a feasible fertiliser program for many slopes and plains areas. In some areas molybdenum, a trace element, may need to be added every 4 to 5 years.

Potash is also commonly deficient on light soils. However, because serradella is deep rooted it can scavenge potash. It is important to seek local advice about the fertiliser requirements for any given district.

Research at Dubbo, Coolah and Binnaway, in central western NSW, has shown that serradella grown on some extremely acidic soils does respond to lime when it is applied at 1 to 2 t/ha. In a long-term farm program, even if the pasture species is an acid tolerant one such as serradella, lime application should be considered for most acidic soils.

Well nodulated serradella fixes significant amounts of nitrogen. It is undesirable and wasteful to use fertilisers containing nitrogen.

Productive serradella pastures probably fix as much soil nitrogen as do effective sub clover or medic pastures. On low fertility soils, good legume pastures commonly fix about 15–20 kg of nitrogen for every tonne per hectare of legume drymatter production. In a legume dominant pasture, properly managed and fertilised, a typical year can result in soil nitrogen improving by about 40 kg/ha. Sometimes in good seasons 100 kg/ha or better nitrogen improvement can be achieved.

Weed control

Serradella can establish and grow adequately with light to moderate weed competition. However, under extreme weed pressure, both establishment and productivity will suffer.

Weed competition in new sowings can be minimised in a number of ways, including the appropriate use of registered pre and post emergent herbicides.

Serradella is more sensitive than sub clover to many herbicides. However, research has shown several herbicides are suitable for use in serradella pastures, for details, consult NSW Agriculture’s latest edition of Weed control in lucerne and pastures.

Many acidic sandy soils are invaded by noxious weeds like sifton bush. A healthy pasture, which comprises a legume such as serradella and a perennial such as Consol lovegrass, is an important component of a program to upgrade these weed infested sites.

Insect pests

Few major insect pests have to date troubled serradella pastures.

Yellow serradella has shown excellent tolerance to blue green aphid (Acyrthosiphon kondoi) and spotted alfalfa aphid (Therioaphis trifolii).

Blue oat mite (Penthaleus major) and red legged earth mite (Halotydeus destructor) can attack and damage newly sown stands of serradella. However, serradella tolerates these pests better than lucerne or sub clover. Heavy infestations in newly sown stands require control.

Lucerne flea (Sminthurus viridus), vegetable weevil (Listroderes obliquus) and jassids (Cidadellidae) are among other pests that can prove troublesome in legume pastures such as serradella. Once serradella plants are past the first true leaf stage (the first pinnate leaf) they are not usually severely attacked by most sucking pests. The small hairs on the leaflets are possibly responsible for repelling the insects.

Native budworm (Helicoverpa punctigera) can prove a major problem at seed set, particularly with late flowering crops.

For control it is important to only use products that are registered.

Diseases

Few disease problems have so far occurred in commercial serradella stands. Brown leaf spot (Pleiochaeta setosa) has been recorded, but little damage has been noted. Grey mould (Botrytis cinerea) was identified at Tomingley in the central west. The disease causes stem lesions and leaf spotting during moist, cool weather. Sclerotinia has been identified in seed crops at Balladoran in the central west.

In southern Queensland Colletotrichum (anthracnose) and Cercospora fungus diseases have been identified in an irrigated crop of Madeira serradella. The damage has been quite severe. Colletotrichum is an important disease of serradella in the Mediterranean region. The extent of the threat of these diseases to the NSW serradella industry is unknown.

Any significant diseases noted in serradella pastures should be checked with NSW Agriculture district agronomists.

Urine patches from livestock can be confused with disease. They appear as circular to semicircular areas usually less than 60 cm in diameter. Plants burn off, are discoloured, and may be severely stunted. They tend to be more significant in dry years.

Grazing management

Properly established serradella will withstand reasonable grazing pressures. Once well established, serradella is suitable for continuous stocking at reasonable stocking rates. More upright varieties can be damaged by heavy grazing if plants are allowed to grow erect and rank before heavy stocking. These varieties grow more prostrate if they are grazed before they grow too upright, and as a result are less vulnerable to heavier grazing.

Avoid overgrazing as it causes land degradation and can lead to soil erosion. Aim to maintain at least around 70 percent ground cover.

Serradella does not seed satisfactorily when it is heavily grazed during flowering and early seed set, especially in the early years of establishment and in seasons with below average rainfall. If a new stand is particularly sparse, only light grazing or no grazing at all is suggested to enable maximum growth and seed pod development. An ungrazed healthy serradella plant can reach a diameter of over 1 m and can set many seeds.

Once the density of serradella is adequate, somewhat harder grazing management may be practised, even during flowering. Hard seed content ensures regeneration if seeding is sometimes missed (because of drought or poor management). However, in western areas where spring and winter conditions are often dry, it is important to encourage reasonable seed set whenever possible.

Graze the stubble before the next autumn germination because large quantities of dry serradella stubble, and perhaps also stubble of other plants such as ryegrass, appear to inhibit germination of serradella seedlings. High residue levels insulate the seed on the ground from the temperature fluctuations that break down hard seed. Without this breakdown re-establishment may be poor.

If summers are wet graze pastures before the autumn break to improve serradella germination.

The first serradella stands sown in NSW are now over 25 years old and continue to thrive.

In paddocks where the soil surface tends to set extremely hard, an occasional shallow cultivation or chisel ploughing on the contour in late summer may encourage autumn germination.

Serradella should be resown after a cropping phase, especially if it has been cropped for longer than 2 years. Seed reserves may have been buried too deeply, and herbicides used in the cropping phase may have prevented regeneration for several seasons. A lengthy cropping phase commonly reduces and can exhaust seed reserves.

Livestock health

Despite extensive areas established, bloat has not yet been recorded in stock grazing serradella pastures.

No oestrogen problems have yet been recorded in livestock grazing serradella pastures.

Nutritional quality and animal production

Serradella is an extremely nutritious pasture legume; it is rich in protein, minerals, and energy. In the vegetative and dry stages it has a similar nutritive value to most sub clover varieties. Serradella makes excellent quality hay and silage.

Because of their deeper rooting habit and ability to respond to later spring rains, serradella pastures tend to stay green and retain quality longer than sub clover pastures.

Proceed to Part E – Serradella seed production.